I want to run my amplifier via batteries and use a TTL driven switch to turn it ON, only when it's needed - to save power. So for +/- 12 volts with 20 mA should i go with FETs or just used mechanical switches?
A couple of MOSFET switches are going to be cheaper, more compact and much less power hungry.
Using a TTL output (switching between 0.4V and around 3.0V) to control a P-channel MOSFET sourcing your +12V and an N-channel MOSFET sourcing your -12V is going to take a little fiddling.
A 1k pull-up resistor from the TTL output to +5V would give you useful extra output swing.
You could use a "logic level" N-MOSFET - gate tied to the TTL output, source tied to 0V and drain tied to the gate of the P-channel MOSFET to control the +12V rail. You will need a resistor (perhaps100k) tied to the +12V supply to make sure that the P-channel MOSFET turns off.
Turning on the -12V rail is a little more difficult. Perhaps the easiest way to do it would to use a second P-channel MOSFET in parallel with the one switching the +12V rail to drive the gate of the N-channel MOSFET driving the -12V rail. Again, you will need a resistor from the drain of the second P-channel MOSFET to the -12V supply to make sure that the N-channel MOSFET is fully off when it is supposed to be off.
On Sep 2, 9:38 pm, " snipped-for-privacy@gmail.com" wrote:
Here you go. This uses a pair of N and P channel mosfets along with some level shifting. It also incorporates current limiting for start up and just in case. Sorry about the limited, lack of, explanation and component values.
Grab hold of LTSpice.....
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